A radio frequency (RF) integrated circuit may include multiple transistor die that are placed in an integrated circuit package by a die attach machine. A robotic bonding tool may be used to wire bond the die to other circuit elements within the package, and to leads of a package leadframe. Such a tool generally includes a surface/wire-feed detection system that detects bond pads or other bond sites of a given die, and determines the height coordinates of these bond pads. The other circuit elements in an RF integrated circuit may include, for example, tuning capacitors.
The wire bonding of the various circuit elements may create several differently-shaped wire bond profiles, depending on the placement of the various circuit elements to be connected by wire bonds. A wire bond profile may be characterized as a side or profile view of a wire extending from a first bond site to a second bond site. In an RF integrated circuit, the wire bonds may carry high frequency signals. Certain types of RF integrated circuits, such as RF power transistors, are tuned through these wire bond profiles. Therefore, it is important for these wire bond profiles to achieve a desired shape for optimal RF performance.
The two major wire-bonding processes used for electronic package interconnects are wedge bonding and ball bonding. The wedge-bonding process has traditionally been used to form the package interconnects of RF integrated circuits due to its ease in forming the wire bond profiles necessary for optimal RF performance, while ball bonding provides a more economical and robust process than that of wedge bonding.
Standard wire bonds of RF integrated circuits are typically parallel to one another in a plan view of the integrated circuit. This parallel configuration results in a high level of mutual coupling capacitance between neighboring wire bonds. For example, on an output side of the integrated circuit, wire bonds are typically packed tightly together, resulting in a substantial mutual coupling capacitance. As the mutual coupling capacitance increases, the stability of the electrical performance and operating bandwidth decreases.
Previous attempts to solve the problem of mutual coupling capacitance included increasing the pitch of, or distance between, wire bonds. While increased distance between wire bonds assists in decreasing the mutual coupling capacitance between wire bonds, fewer wires are able to fit on the circuit elements, resulting in fewer wire bonds used in the integrated circuit. A smaller number of wire bonds in the integrated circuit is problematic for RF integrated circuits because it causes a higher series resistance and less tuning resolution for obtaining the resonance frequency.
Thus, a need remains for techniques for minimizing the effect of the mutual coupling capacitance between wire bonds in an integrated circuit.